In a statement, Crossrail's programme director Andy Mitchell said: "Crossrail had identified that significant operational cost savings, running into tens of millions, can be realised for taxpayers by introducing rolling stock to the rail network over a shorter period of time.

"As a consequence of the shorter delivery timescales, contract award is not required until 2014 and therefore the issuing of tender documents can be deferred, allowing the conclusions of the Government's review of public procurement to be taken into account."

The announcement was met with anger by critics who questioned why the review could not be applied to the Thameslink contract, which was finalised in June.

Maria Eagle, Labour's shadow transport secretary, said: "The Tory-led Government announced a one-year delay to Crossrail in the spending review to take £1bn out of the costs, so this is nothing but spin.

"If ministers are now saying it's possible to review the Crossrail contract, they must explain why they have cost British jobs by refusing to do the same for the new Thameslink trains as Labour has repeatedly demanded."

Bob Crow, trade union RMT's general secretary, added: "This is an admission by the Government that they got the Thameslink contract wrong.

"They should now do the decent thing and award that work to Bombardier in Derby before it is too late."